1. Field of the Invention
The present invention relates to an optical information recording reproduction device that performs record operation of a signal into an optical recording medium using a laser beam, and more specifically relates to an optical information recording reproduction device in which an excellent record grade is achieved by stably performing aberration detection.
2. Description of the Related Technology
Recording information into an optical recording medium such as optical disk is performed in the following way. First, recording data are modulated by the EFM (Eight to Fourteen Modulation) method or the 8-16 Modulation method, and then a record pulse is formed based on the modulated signal. Then, intensity or irradiation timing of a laser beam is controlled based on the record pulse, so that a record pit is formed on the optical recording medium.
In the optical information record, numerical aperture (NA) of an object lens is effectively increased for record reproduction of the optical recording medium having high density and high capacity. For such optical recording with high density and high capacity, an allowable variation range of a beam spot diameter is extremely reduced, in addition, allowable manufacturing errors of the optical recording medium and a pickup device (thickness and warp in a medium, and lens tilt and the like in a pickup) must be extremely reduced.
In a usual optical information recording reproduction device, regarding allowable manufacturing errors of the optical recording medium and pickup device, there is a problem of aberration generation due to the manufacturing errors.
As an example of a method of suppressing the aberration generation, a method is proposed (JP-A-9-197264 “Real Optical System Having Disk Substrate with Variable Thickness”: MARK CO., LTD.), in which a first negative lens and a second positive lens are disposed in this order after a collimator lens, and when thickness of a substrate of an optical recording medium is increased, an interval on a light axis between the first negative lens and the second positive lens is decreased, and when thickness of the substrate of the optical recording medium is decreased, the interval on the light axis between the first negative lens and the second positive lens is increased, thereby aberration generation is suppressed. Moreover, a method is proposed (JP-A-2004-103093 “Optical Pickup and Optical Information Processor Using the Same: Ricoh Company, Ltd.), in which a distance between an object lens and an attachment lens is optionally changed in correspondence with thickness of a substrate of an optical recording medium using a pickup having a mechanism for detecting a wave front configuration, thereby aberration is suppressed.
Furthermore, a recording medium recording reproduction device and a recording medium record reproduction method disclosed in JP-A-09-251662 disclose a player and a method in which a spherical aberration due to an error of thickness of a substrate of an optical recording medium is reduced in a pickup having a second group lens, so that an excellent reproduction signal is obtained.
To achieve an excellent record grade in the optical information recording reproduction device, optimization of a diameter of laser beam spot irradiated onto an optical recording medium, selection of strategy optimized for a laser spot and an optical recording medium, and suppression of aberration generated due to a manufacturing error are important items.
While the JP-A-9-197264 “Real Optical System Having Disk Substrate with Variable Thickness: MARK CO., LTD.” shows a unit of correcting aberration, it does not refer to a method of detecting the aberration.
The JP-A-09-251662 entitled “Recording Medium Recording reproduction device and Recording Medium Record Reproduction Method: Sony Corporation” shows a method of detecting thickness of a substrate of an optical recording medium in detection of a focus error (FE) signal. However, separation detection of spherical and coma aberrations is expected to be difficult in the focus error signal.